The occurrence of trans isomers of unsaturated fatty acids in human aorta is being measured by gas liquid chromatography and the content will be related to the severity of atheromata. The influence of trans isomers upon the metabolism of fatty acids will be assayed by their inhibition of tissue enzyme reactions using the entire series of trans 18:1 acids as substrates or as inhibitors. Reactions to be studied will include desaturase, chain elongation, chain shortening, acyl interchange, and acyl incorporation into PL, and TG using liver microsomes from normal and essential fatty acid deficient rats. The influence of trans isomers upon lipolytic reactions will be studied using pancreatic lipase and cholesteryl esterase. The effects of high dietary trans acids upon desaturase and chain elongation will be studied in rats.